Executive brief
A vulnerability exists in the Linux kernel's SMB client, which is used to connect to network file shares. A race condition during the unmounting of a file system can lead to a system crash or potential unauthorized access. This occurs because the system attempts to use memory that has already been freed during the shutdown process.
Technical details
A race condition in cifs_oplock_break() leads to a use-after-free (UAF) of the cinode structure. When unmounting, _cifsFileInfo_put() may release the final reference to the superblock, triggering immediate inode eviction and RCU-based cleanup. If cifs_oplock_break() continues to access the cinode after this cleanup, a UAF occurs. The fix involves holding an extra reference to the superblock (cifs_sb_active) throughout the oplock break operation to ensure the cinode remains valid.
Affected products
- Linux Linux Kernel 3.16.72 to 3.17, 4.9.171 to 4.10, 4.14.114 to 4.15, 4.19.37 to 4.20
Timeline
- 2025-08-16: advisory: Vulnerability published in NVD
References
- https://git.kernel.org/stable/c/09bce2138a30ef10d8821c8c3f73a4ab7a5726bc
- https://git.kernel.org/stable/c/0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b
- https://git.kernel.org/stable/c/2baaf5bbab2ac474c4f92c10fcb3310f824db995
- https://git.kernel.org/stable/c/4256a483fe58af66a46cbf3dc48ff26e580d3308
- https://git.kernel.org/stable/c/705c79101ccf9edea5a00d761491a03ced314210
- https://git.kernel.org/stable/c/da11bd4b697b393a207f19a2ed7d382a811a3ddc
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html